Truck and bus suspensions utilize at least one torque rod to secure the drive axle to the vehicle's frame. The securing of the drive axle to the vehicle's frame by the torque rod maintains the drive axle's alignment to the vehicle's frame, it maintains the proper suspension geometry for the vehicle, and it allows free suspension movements in jounce and rebound for all terrain, road and driving conditions. Because of the wide range of dynamic operating conditions for these vehicles, especially heavy duty trucks, the severe impact loads to the suspension system combined with the road induced vibrations on the suspension system lead to a deleterious effect on the individual suspension components including the torque rods as well as having a negative impact on the operator's physical fatigue condition. These severe dynamic conditions can accelerate wear of the torque rods of the suspension system leading to premature failures of these torque rods.
The purpose of torque rods on large vehicles is to stabilize the axle. They prevent the axle from rotating about its axis; they prevent the axle for moving fore and aft during braking and acceleration; and they prevent axle yaw. While there are a variety of suspension designs, one of two approaches are generally used to stabilize the axle. The first approach uses straight rods with pivotal joints at either end. Two of these straight rods are mounted fore and aft on the vehicle; where one end is mounted to the axle and the other end is mounted to the frame. A third straight rod is similarly mounted laterally in the vehicle, generally perpendicular to the other two. The second approach is a V-configuration torque rod assembly. This type of torque rod has pivotal joints at the apex of the V as well as at the ends of the legs. The apex is mounted to the axle, and the legs are mounted to the frame. The V-configuration controls both fore-aft movement as well as lateral movement. The major advantage of the V-configuration rod assembly is axle stability.
A typical prior art single or V-configuration torque rod is comprised of two or three pivotal joint eyelet forgings rigidly connected with tubes to provide the mechanical integrity. The eyelets and tubes form a natural path for shock and vibration energy to transfer from the suspension system into the frame, the cab and other areas of the sprung mass of the vehicle. In order to intercept this path, attempts have been made to incorporate an isolation function into the pivotal joint design. This isolation function thus makes the pivotal joint a critical multi-functional component for the torque rod assembly as well as the suspension system as a whole.
These prior art torque rods have been designed as MIG welded tube to tube designs, resistance and MIG welded tube to tube designs, cast designs, polymer designs as well as other types of construction. Designs which incorporate solid rods, which are cheaper, were not able to be developed due to the fact that the diameter of the solid rod was too small to be connected to the pivot joints and still maintain an acceptable eye flexure and fatigue life. The tube designs, being larger in diameter, offered a larger radius at the point of welding to the pivot joints thus significantly improving the flexure and fatigue strength of the assembly.
The continued development of torque rod assemblies has been directed towards lower cost designs which offer equivalent or better performance characteristics.